Alvin, a sales representative for a company making industrial solvents, lost a major customer last month. Until then, Alvin's year has been about average in the level of sales. Early in the year, Alvin brought in two new customers of about the size of the customer he lost last month. Alvin's supervisor gives Alvin an unsatisfactory rating in his annual performance appraisal. It is likely that Alvin's supervisor has committed the _______________ error.